Throughout human history, people have utilized caves for protection from the elements, as safe havens from predators, and as canvases to display beautiful works of art. Now, a group of scientists from Vanderbilt University are using caves to learn about weather patterns in the past. And what they're discovering may provide insight into our planet's future climate.
Caves serve as geological time capsules. As water seeps down into the ground, it collects minerals, mainly calcium carbonate, that form layers in stalagmites. During wet periods, these deposits, known as speleothems, grow. During dry periods, they form dusty skins, and it's this vacillation in layers of speleothems that provides a chronology of past climate.
The thickness of each layers depends on the amount of water seeping into the cave (which is dependent on rainfall), and the concentration of carbon dioxide in the cave's atmosphere. By recording the varying thickness of each layer and then dating the layers, geologists can reconstruct wet versus dry periods in the past. By analyzing ratios of oxygen isotopes in the layers, they can also track changes in temperature at the point when the water was originally condensed into droplets. So the caves serve as climate proxies for temperature and rainfall over time.
The team, which included Jessica Oster, an assistant professor of earth and environmental sciences at Vanderbilt University, traveled to one of the rainiest places on Earth to test their analyses. Mawmluh Cave is nestled within the East Khasi Hills district of northeastern India. They wanted to see if they could corroborate weather patterns deduced from the cave's speleothems to written records of India's monsoon seasons over the past 50 years. And what they found was a perfect match.
"Now that we have shown that the Mawmluh cave record agrees with the instrumental record for the last 50 years, we hope to use it to investigate relationships between the Indian monsoon and El Niño during prehistoric times such as the Holocene," Oster says.
Between six and nine thousand years ago, the Earth experienced what is known as the Holocene Climate Optimum, a period of warming that produced temperatures averaging between four and six degrees Celsius higher than they are today. Climate scientists predict a return to these temperatures if greenhouse gasses from human activity continue to build.
If scientists can use mineral deposits in caves to reconstruct weather patterns during the Holocene Climate Optimum, it may provide insight into future weather patterns on our warming planet.
The team's research was publish on May 19th in the journal Geophysical Research Letters.